This open-label multiple dose non-randomized study is undertaken to determine steady state pharmacokinetic (PK) and pharmacodynamic (PD) profiles of donepezil hydrochloride (Aricept) in patients with impaired renal function and in healthy subjects. Subjects with renal impairment will be age, gender, and weight matched with healthy subjects. A total of 16 patients with renal impairment and 16 subjects with normal renal function from two sites will be enrolled, with each site completing 8 subjects in each group. Subjects will be involved in the study for 7 weeks. Procedures will be done outpatient and inpatient and include:1) screening and safety lab evaluations, 2) screening and safety physical exams, 3) two (2) day General Clinical Research Center (GCRC) hospitalizations, and 4)PK and PD blood samples collected throughout the study period. The study aims to demonstrate safety and tolerance of the drug (Aricept) in renal impaired patients.